Material used in the channels surrounding automobile glass needs good abrasion resistance to assure proper sealing of the automotive glass to avoid both leaks and freezing around the glass in cold weather.
Automotive weatherstripping for doors and trunk lids ordinarily uses closed-cell extruded EPDM sponge. A typical compound contains an EPDM polymer with high ENB (ethylidene norbornene) to provide a fast cure rate. EPDM (ethylene-propylene-nonconjugated diene terpolymer) is the industry standard for use as weatherstripping, made by the copolymerization of ethylene, propylene and ethylidene norbornene. Advantages in using this formulation include high molecular weight which imparts good green strength for cross-sectional shape retention.
It is customary for automotive weatherstripping to be coated with silicone or urethane spray to impart a low coefficient of friction surface for easy door closure and freeze release. This is to prevent automobile doors and trunk lids from freezing shut at low temperatures.
The silicone/urethane coating procedure has been problematic for weatherstripping manufacturers because of additional handling operations required, additional manufacturing costs, and inconsistent performance of the coating in actual field service.
The weatherstripping material is subject to extreme wear due to rubbing from repeated opening and closing of doors, windows and trunk lids. This abrasion can result in removal of sprayed coatings and ultimate failure of the weatherstripping material.
Since it is necessary to promote freeze release of automotive weatherstripping this invention accomplishes this and bypasses the need for a sprayed coating by allowing the freeze release properties to be obtained by co-curing the EPDM/Silicone/erucamide onto the surface of the weatherstripping.
A further enhancement of the improved properties results from modification of the silicone-modified EPDM/erucamide with carbon, as certain graphites. The experimental data that follows indicates that the addition of these graphites lowers the coefficient of friction to a level below that specified by automotive manufacturers for weatherstripping.
Improvements to the freeze-release and coefficient of friction properties of weatherstripping have been attempted by changing the composition of the weatherstripping itself. An EPDM silicone blend surpasses EPDM sponge with a low coefficient of friction, greater resistance to surface freezing, and excellent weathering resistance. Silicone-modified EPDM may be used in weatherstripping for automotive doors, trunks, and sunroofs and for continuous and molded automotive sponge. However, this material is not routinely used as a material of construction for general purpose automotive weatherstripping. One reason for this is the higher cost of this material as compared to EPDM sponge.
Other materials which have been used for automotive weatherstripping are silicone sponges, which have been used for higher-temperature resistant automotive sunroof seals and related sponge gasketing requiring a similar type of heat resistance. This material is prohibitively expensive for general automotive weatherstripping use.
The instant invention represents a cost savings by (1) imparting the necessary freeze release and coefficient of friction properties to EPDM sponge by co-curing a thin-skin of the high performance silicone-modified EPDM based material of this invention onto the EPDM sponge; and (2) eliminating the need for sprayed urethane or silicone coatings to impart the needed surface properties to the weatherstripping.
A further advantage of the current invention is that since the improved properties are imparted during cure, they will not erode away as will the commonly used sprayed coatings. A still further advantage of cocuring the freeze release agent over post-manufacture spraying is the environmental advantage gained by eliminating the spraying process. The current invention eliminates the need for organic solvents necessary to dissolve the silicone and urethane.
An approach to abrasion resistant coatings for automotive weatherstripping that are not sprayed include that of Chihara et al (in U.S. Pat. No. 4,720,518) wherein amide-functional thermoplastic polymer solutions are halogenated and then blended with silicones, fillers and pigments and coated onto a rubber substrate in the form of a weatherstrip or glass run channel, dried and irradiated with ultraviolet light or heated sufficiently to reform the amide groups and to provide the rubbery substrate with an adherent and abrasion resistant coating with a reduced coefficient of friction.
The current invention employs neither amide-containing resins as nylon nor ultraviolet irradiation described in this invention.
Advantageous performance properties of synthetic rubber compositions are described by Itoh et al in U.S. Pat. Nos. 4,201,698 and 4,150,010. Described therein are synthetic organic rubber and organopolysiloxane capable of co-vulcanization onto an elastomer with improved Properties compared to natural and other synthetic organic rubbers.